I do it (maybe) in a little more practical way:
- My pinhole camera (Zero 45) has many different focal lengths and pinhole diameter combinations, and
- My meter measures up to F32. (Sekonic L-208)
- I meter for F32 then multiply this with a factor determined before (more on this below), and then
- If the resulting exposure time exceeds 1 sec. I further adjust it for reciprocity failure using this (Ilford) formula: New time = Calculated time ^ 1.48 or in Excel notation: New time = POWER(Calculated time, 1.48)
It's hard to remember and calculate each factor, therefore I prepared a simple Excel chart, printed it, and had it laminated with PVC. I keep this chart (and a scientific calculator) with the camera all the time...
See the chart (and the two formulas that I've used) below:
Hope this helps if you ever need to make your own practical exposure calculation charts,
P.S. Beware, the reciprocity failure correction formula applies only to Ilford B&W films!
Last edited by Loris Medici; 05-31-2013 at 03:55 AM. Click to view previous post history.
Reason: Added P.S.